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Skin T1 mapping at 1.5T, 3T, and 7T

1. 2. # 4451 Presentation: Thursday @ 2pm. Skin T1 mapping at 1.5T, 3T, and 7T. Joëlle Barral 1. Peter Stoica 2. Dwight Nishimura 1. Nikola Stikov 1. Maryam Etezadi-Amoli 1. Erik Gudmundson 2. In a nutshell. In vivo skin T1 :.

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Skin T1 mapping at 1.5T, 3T, and 7T

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  1. 1 2 # 4451 Presentation: Thursday @ 2pm Skin T1 mapping at 1.5T, 3T, and 7T Joëlle Barral 1 Peter Stoica 2 Dwight Nishimura 1 Nikola Stikov 1 Maryam Etezadi-Amoli 1 Erik Gudmundson 2

  2. In a nutshell • In vivo skin T1: • Affected by: temperature and perfusion • Gold standard: 2D-Spin Echo Inversion Recovery • Model: • Fitting procedure: non-linear LS + grid search

  3. Epidermis ~ 100 μm Dermis ~ 1 mm Hypodermis (fat) ~ 1 cm Motivation & Goals For skin imaging, does increase in T1 at higher field strengths offset the SNR gain? • Define a T1 mapping gold standard methodology • Determine T1 of the different skin layers http://www.nlm.nih.gov Barral JK, et al. Proc 16th ISMRM, p. 742, 2008

  4. Pulse sequence 2D Spin Echo Inversion Recovery SE-IR with a 8.64 ms Silver-Hoult adiabatic 180°* θ1 90° 180° TI TR * A selective pulse was used for Subject 1 and a non selective one for Subject 2. Transition bands decrease the effective flip angle when a selective pulse is used. In both cases, the effective flip angle at each location depends on T1 and T2. http://www-mrsrl.stanford.edu/SpinBench

  5. Fitting procedure Generic model ‘ab’: Complex data Find a, b, and T1 by minimizing The model is linear in a and b. This makes it possible to rewrite J so that an estimate of T1 is found through a 1D grid search over possible T1s Stoica P and R Moses. Spectral Analysis of Signal, p. 151, 2005

  6. 20C±2.5C* 68F±4F 1.5T, 3T and 7T Calf immobilized Room temperature Protocol 1/2 Receive-only @ 1.5T and 3TTransmit/Rc @ 1.5T and 7T 1 inch ∅ *Variations between experiments. Temperature was stable within 1C for a given experiment.

  7. Protocol 2/2 We target T1s < 1000 ms. TI = [50, 300, 1000, 2000] ms Resolution: 117μm × 469μm × 2mm

  8. Results: Example at 3T (1/3) Individual magnitude images TI 50 ms 300 ms 1000 ms 2000 ms Muscle Hypodermis Dermis

  9. Results: Example at 3T (2/3) SNR map @ TI = 2000 ms T1 map [ms] Muscle Muscle Dermis Dermis Hypodermis Hypodermis

  10. Results: Example at 3T (3/3) T1 histograms # pixels ms Muscle* Hypodermis Dermis *Muscle is not visible when a Tx/Rc coil is used

  11. Results: summary Error bars indicate the standard deviation over the ROI, taken as 0.64xFWHM.

  12. Comparison with the literature Muscle Hypodermis (used saturation recovery) Richard S, et al. J Invest Dermatol 97:120-125, 1991 -- Gold GE, et al. AJR 183:343-351, 2004 -- Stanisz GJ, et al. MRM 54: 507-512, 2005

  13. Conclusions • In the dermis, T1 mapping is still very challenging: - short T2 - presence of many structures - temperature differences • A 94 % increase in hypodermis T1 was observed from 1.5T to 7T. It translates to a 40% decrease in SNR efficiency for our skin protocol. It should therefore not offset the expected field-strength related SNR increase. • The fitting algorithm we proposed can be generalized to other relaxometry techniques. Barral JK, et al. Proc 16th ISMRM, p. 742, 2008

  14. Thank you! Contact: jbarral@stanford.edu “Skin imaging at 7T” poster #1993, Wednesday @ 1:30 pm

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